How do I get out of a node group?
To enter and exit a node group press Tab

(Think of it like entering/exiting Edit Mode for node groups) 

Form the manual:


  With a group node selected, Tab expands the node to a window frame, and the individual nodes within it are shown. You can move them around, play with their individual controls, re-thread them internally, etc. just like you can if they were a normal part of your editor window. You will not be able, though, to thread them to a node outside the group; you have to use the external sockets on the side of the group node. To add or remove nodes from the group, you need to ungroup them.